Thursday, September 10, 2020

Chapter 6 : DC Machines-Page 5

Chapter 6 : DC Machines

41. For wave winding, the average pitch
A. must be odd
B. must be even 
C. may be odd or even
D. must be fractional

... Answer is (B)



42. Which of the following is Closet to the armature circuit resistance of a dc generator
A. 2 W
B. 20 W
C. 2000 W
D. 200 W

... Answer is (A)


43. Hysteresis losses in a dc generator are basically due to

A. initial energy to magnetise the core
current flowing in the armature
C. reversal of magnetism of the armature core

D. None of these

... Answer is (C)



44. Hysteresis loss proportional to ses in a de machine are

A. 1/N
B. N
C. N²
D. 1/N

  ... Answer is (B)


45. Eddy current losses in a dc machine varies as
A. 1/t 
B. 1/t²
C. t
D. t²
Answer is (D)


46. Hysteresis loss in DC machine varies as
B. 1/f
C. f²
D. 1/f

  ... Answer is (A)



47. A dc generator operates at constant speed, variable load, Which of the following losses is likely to be most significant?
copper loss
B. bearing friction loss

windage loss
D. eddy current loss

  ... Answer is (A)


48. A DC simplex lap winding
A. is a completely closed winding
B. has a minimum number of brushes
C. has a number of parallel paths equal to the number of poles
D. has all the above features

... Answer is (D)


49. In a dc generator, windage loss is proportional to

A. square of armature speed
B. armature speed

supply voltage
D. square of supply voltage
  ... Answer is (A)


50. Iron losses in a DC machine take place in  

A. yoke
B. commutator
C. armature rotor
D. armature conductors

  ... Answer is (C)



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